Redesigning Hulls

Discussion in 'Boat Design' started by doogymon, Oct 26, 2007.

  1. doogymon
    Joined: Jul 2006
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    Location: Ontario

    doogymon Junior Member


    I have a crazy idea. I'd like to modify a boat like a Chrysler 22' to a Plumb Stem. I like the Falmouth working boat hulls in the UK but don't want to sell the farm for one and shipping is out of the question unfortunately..
    While I am at it I'd like to explore the possibilties of adding (somehow), faux lapstrake, wide planks.

    Do I have to go to Naval Architect School for this?


  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Both can be done, though the fake lapped planking will be the most difficult. Both ideas will add weight, which is the enemy of all sailboats, especially the old Chrysler 22, which was heavy to begin with.

    A plumb bow would require the forward quarter of the boat (around the first 5' of hull) to be refaired to the new bow shape. Since you really can't just cut it back and 'glass it plumb, you'll need to extend the waterlines forward to the new stem location. This will introduce an excessive amount of hollow, unless you are particularly gifted. You can slap on some closed cell foam and sheath this, make molds, maybe C-Flex, possibly wood core, there are a variety of methods to approach this.

    This is a major undertaking. The deck cap would likely have to be removed, though it could be just pried up enough to allow fairing. I suspect you'll alter the balance of the yacht slightly, though rig tuning may fix this if the waterlines aren't dragged out too far and you haven't picked up too much displacement forward. This isn't that uncommon a task. I know of a few that have done similar, of course all were larger boats and one was trying to get his 38' boat, into an ocean race that was limited to 40'ers and over.

    The lapped planking will be problematic to say the least. Foam planks with a tapered backside, maybe wooden ones of similar shape. The basic problem is how to 'glass these planks into the hull shell. Lapped boats don't sheath well, unless the lap is heavily rounded, which defeats the looks considerable. Wooden planks could be just glued in place, but I can assure you these will be the more difficult pieces of wood you've ever made.

    Go for the plumb stem and stick a sprit and new rig on the old girl. These are reasonably doable things. She'll have the channel cutter look. You could route (very lightly) into the hull shell to simulate carvel plank seams. Set you 1/8" router bit to just remove the gel coat, then epoxy over this to seal it.

    The new rig will require a hand to guide the arrangement and balance over the existing hull and appendages. While they're at it, they could draw up a new bow shape, so you could build templates from.

    Naturally, after these conversions, the once stylish, now dated cabin on the Chrysler will look out of place, so you may consider a new deck and trunk cabin to suit the new look.
  3. alan white
    Joined: Mar 2007
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    Location: maine

    alan white Senior Member

    PAR said it all---- I would only add that it might be a good finishing touch to add 1/8" thick spiled fore and aft "planks" of something like spanish cedar, or an American cedar to simulate very convincingly the look of a carvel hull. you would roughen the gelcoat, epoxy the planks, and longboard. The advantages would be looks, strength, buoyancy, and mostly, a way to bring together the original hull with the new appendage in a way that is more self-fairing.


  4. doogymon
    Joined: Jul 2006
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    Location: Ontario

    doogymon Junior Member

    Thanks Par and company.

    Thanks for response.

    I may just go for it.


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